Cell Membranes and Transport May/June 5 (b) Name two assimilates that move from the palisade mesophyll cells to the vascular tissue to be exported from the leaf. For Examiner’s Use 1 ....................................................................................................................................... 2 .................................................................................................................................. [2] (c) Explain, using the term water potential, how water moves from the vascular tissue to the atmosphere. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [4] [Total: 12] © UCLES 2005 9700/02/M/J/05 [Turn over Cell Membranes and Transport May/June For Examiner’s Use 12 6 Fig. 6.1 shows a diagram of a plasma (cell surface) membrane. K L M N Fig. 6.1 (a) Indicate, by putting a circle, membrane shown in Fig. 6.1. 0.7 nm 7.0 nm 70 nm , around one of the following, the width of the 7 × 10–5 m 700 µm 7.0 µm [1] (b) Outline the functions of the following components of the plasma membrane. K ...................................................................................................................................... .......................................................................................................................................... L ...................................................................................................................................... .......................................................................................................................................... M ...................................................................................................................................... .......................................................................................................................................... N ...................................................................................................................................... ......................................................................................................................................[4] © UCLES 2007 9700/02/M/J/07 Cell Membranes and Transport May/June 13 (c) Some substances may cross plasma membranes by simple diffusion. Glucose, however, does not. For Examiner’s Use Explain why glucose cannot pass across membranes by simple diffusion. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[2] (d) In an investigation, animal cells were exposed to different concentrations of glucose. The rate of uptake of glucose into the cells across the plasma membrane was determined for each concentration. Fig. 6.2 shows the results. rate of uptake of glucose by cells / arbitrary units 22 20 18 16 14 12 10 8 6 4 2 0 0 5 10 15 20 25 30 35 40 concentration of glucose / arbitrary units Fig. 6.2 Using the information in Fig. 6.2, explain how the results of the investigation support the idea that glucose enters cells by facilitated diffusion. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[2] QUESTION 6 CONTINUES ON PAGE 14 © UCLES 2007 9700/02/M/J/07 [Turn over Cell Membranes and Transport May/June For Examiner’s Use 14 (e) State how active transport differs from facilitated diffusion. .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[1] [Total: 10] © UCLES 2007 9700/02/M/J/07 Cell Membranes and Transport May/June 12 5 Fig. 5.1 shows part of a transverse section of a leaf. For Examiner’s Use Q R Fig. 5.1 (a) Explain, in terms of water potential, how water moves from Q to R. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ...................................................................................................................................... [4] © UCLES 2009 9700/02/M/J/09 Cell Membranes and Transport May/June 11 5 (a) Fig. 5.1 represents a molecule of a triglyceride. For Examiner’s Use Name the components A and C and name the bond B. Write your answers on the dotted lines provided in Fig. 5.1. A ......................................................... B ......................................................... C ......................................................... Fig. 5.1 [3] (b) A phospholipid is sometimes described as a modified triglyceride. (i) State how the structure of a phospholipid differs from a triglyceride. .................................................................................................................................. .................................................................................................................................. .............................................................................................................................. [2] (ii) Explain how a phospholipid is suited to its role in cell membranes. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .............................................................................................................................. [3] © UCLES 2011 9700/22/M/J/11 [Turn over Cell Membranes and Transport May/June 4 2 Fig. 2.1 shows a drawing made from an electron micrograph of two adjacent cells in a leaf. A B C D E F G vacuole Fig. 2.1 (a) Structures A and B are both visible using the light microscope, but the internal detail of these organelles shown in Fig. 2.1 is only visible using the electron microscope. Explain why the internal details of structures A and B are only visible when using the electron microscope and not when using the light microscope. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ...................................................................................................................................... [3] © UCLES 2012 9700/21/M/J/12 For Examiner’s Use Cell Membranes and Transport May/June 5 (b) Name in full the structures labelled C, D and E. C ....................................................................................................................................... For Examiner’s Use D ....................................................................................................................................... E ................................................................................................................................. [3] (c) State one role of vacuoles in plant cells. ..................................................................................................................................... [1] (d) Structures F and G have very different permeability properties. Explain how the composition of structures F and G determines the permeability properties of these structures. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [4] (e) Fig. 2.1 shows two plasmodesmata connecting the adjacent cells. Describe the roles of plasmodesmata in transport in plants. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] [Total: 14] © UCLES 2012 9700/21/M/J/12 [Turn over Cell Membranes and Transport May/June 2 1 One role of the cell surface membrane is to control the entry and exit of substances. (a) Complete Table 1.1 to show the transport mechanisms across cell surface membranes and examples of materials transported. Table 1.1 transport mechanism across cell surface membrane active transport example of material transported across membrane sodium ions oxygen molecules bacteria exocytosis mucin (for mucus) facilitated diffusion osmosis [2] © UCLES 2012 9700/22/M/J/12 For Examiner’s Use Cell Membranes and Transport May/June 3 (b) Each transport mechanism across cell surface membranes has a characteristic set of features. For Examiner’s Use In each of the boxes below, state one example of a transport mechanism that matches the pathway shown. passive yes active specific transport protein involved passive no active [4] [Total: 6] © UCLES 2012 9700/22/M/J/12 [Turn over Cell Membranes and Transport May/June 10 5 Fig. 5.1 shows a section of a cell surface membrane. For Examiner’s Use P Q W R Fig. 5.1 (a) State the functions of structures P, Q and R. P ...................................................................................................................................... .......................................................................................................................................... Q ...................................................................................................................................... .......................................................................................................................................... R ...................................................................................................................................... ..................................................................................................................................... [3] (b) Circle the width of the membrane shown as W in Fig. 5.1. 17.0 μm 1.7 μm 0.7 μm 70.0 nm 17.0 nm 7.0 nm 0.7 nm [1] (c) Membranes, such as the cell surface membrane, are described as having a fluid mosaic structure. Explain what is meant by the term fluid mosaic. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [2] © UCLES 2013 9700/21/M/J/13 Cell Membranes and Transport May/June 11 (d) Aquaporins are membrane channel proteins in plant and animal cells. They permit the movement of water across membranes. Explain why they are necessary. For Examiner’s Use .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] [Total: 9] 6 (a) Explain how uncontrolled cell division can result in cancer. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] (b) Describe the experimental evidence that shows that smoking causes lung cancer. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] © UCLES 2013 9700/21/M/J/13 [Turn over Cell Membranes and Transport May/June 10 In some organisms, trehalose is used as an energy store and gives protection against the harmful effects of very low temperatures. Trehalose is sometimes referred to as a cryoprotectant, allowing organisms to survive in freezing conditions. Freezing temperatures can damage the cell surface membrane and membranes within the cell. (c) Explain the importance of the cell surface membrane to cells. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] (d) Freezing temperatures can also completely stop enzyme activity by causing the molecules to undergo ‘cold denaturation’. Enzyme activity is not recovered when temperatures are increased to a normal working temperature range. (i) Explain the mode of action of enzymes. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [3] (ii) Suggest how the molecular structure of the enzyme changes during ‘cold denaturation’. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................. [2] © UCLES 2013 9700/22/M/J/13 For Examiner’s Use Cell Membranes and Transport May/June 3 (c) The membrane surrounding the vacuole, called the tonoplast, has a fluid mosaic structure. For Examiner’s Use Describe the structure of this membrane. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [4] (d) Palisade mesophyll cells have very large vacuoles. Explain how water moves from the xylem in the leaf into these vacuoles. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [3] [Total: 12] © UCLES 2013 9700/23/M/J/13 [Turn over
